The field of the disclosure relates generally to gas turbine engines and, more particularly, to a method and apparatus for active clearance control in gas turbine engines.
At least some known aircraft engines generate heat during operation in various internal components, such as, but, not limited to, a high pressure compressor, which includes a rotor disk, compressor blades coupled to the rotor disk, and a casing housing the high-pressure compressor. Differential thermal expansion of the disk, compressor blades, and compressor casing change the clearance between the tips of the compressor blades and the inner surface of the compressor casing. Engine inefficiencies occur when the clearance between the compressor blade tips and the inner surface of the compressor casing is large, thereby facilitating decreased compressor pressure rise capability and decreased stability. Active clearance control maintains the clearance between the compressor blade tips and the inner compressor casing. At least some of the known methods for controlling the clearance between the compressor blade tips and the inner compressor casing are active thermal control and active mechanical control. For example, some known active thermal control methods use compressor bleed air and fan exhaust air to cool the inner compressor casing. Compressor bleed air and fan exhaust air are directed to the outer radial surface of the inner compressor case. The compressor bleed air and fan exhaust air cool the inner compressor casing. The active thermal control method has a slow thermal response.
In addition, some known active mechanical control methods use linkages and actuation to control the clearance between the compressor blade tips and the inner compressor casing. Segmented shrouds attached to a unison ring and actuators individually control the positioning of each shroud. The active mechanical control method has a quick response rate, but the additional equipment required for the active mechanical control method adds weight to the aircraft.